The utility of mice to study mammalian pathology is facilitated by the availability of individuals with a defined genetic background and the opportunities for molecular manipulation of the genome. The primary objectives of the research presented are to exploit these characteristics and develop the mouse as a model system to study eosinophil effector function. The objectives of the research presented herein are to characterize and define the eosinophil-specific promoter and to generate transgenic lines of mice contrived to enable an effective and more precise definition of the role(s) of cytokine growth factors and cell surface molecules in eosinophil differentiation and immunological activation. The specific aims of this proposal are (1) Isolation of genomic sequences coding for the mEPO gene and the characterization of the promoter region/CIS-acting regulatory elements controlling eosinophil-specific expression. (2) The use of eosinophil specific promoters in transgenic mice to express unique markers in cells of this lineage. The proposed experiments are designed to augment observations from the current literature and to provide a foundation for our long-term goal of defining effector function.